IPTV networks in metro areas have a hierarchical structure. At the top of this hierarchy, shown in FIG. 1, is a Video Hub office (VHO) 19 where all video contents are stored in video servers. The VHO 19 is connected to several Intermediate Offices (IO) 18, every IO 18 is connected to several Central Offices (CO) 16, every CO 16 is connected to several Digital Subscriber Line Access Multiplexers (DSLAMs) 14, and every DSLAM 14 is connected to a certain number of subscribers 12.
In an IPTV network, Video on Demand and other video services generate large amounts of unicast traffic from VHO 19 to subscribers 12 and, therefore, require additional bandwidth and equipment resources in the network. To reduce this traffic (and overall network cost), part of video content (e.g. most popular titles) may be stored in caches 15 closer to subscribers, e.g., in DSLAM 14, in service switches at COs 16, or in service routers at IO 18.
On one hand, cache memory has a cost, but on another hand, caching of video content allows decreasing amount of traffic from upstream levels of this hierarchy and, therefore decreasing of network cost. Cache effectiveness is defined as the hit rate, i.e. the ratio of traffic that is served from the cache to the total amount of requested traffic. Hit rate depends on size and throughput of the cache, statistical characteristics of the traffic (e.g., popularity distribution of different titles, their bit rate, size in memory) and on a caching algorithm. For an ideal caching algorithm, the cache size and statistical characteristics of the traffic define hit rate.
Another important factor is granularity of network elements. In case of cache that means that cache is allocated in units whose size does not exceed some limit; cost of cache includes cache unit cost and cost per unit of memory. In case of equipment (switches, routers), cost includes unit cost, I/O module (IOM) cost, Model Driven Architecture (MDA) cost and port cost. The number of ports, MDA, IOMs and equipment units are defined by traffic as a part of the dimensioning process. There is a limited number of IOMs per equipment, and these resources should be shared by the MDAs and cache units.
Overall, to find an optimal (in terms of network cost) location and amount of cache memory is a complex optimization problem.
What is required is a system and method for optimizing a cache arrangement in an IPTV network.